The present invention relates generally to an isolation circuit in a computer system. More particularly, the present invention relates to an isolation circuit enabling an expansion component to operated properly in a low-power mode.
A computer system supplied by a computer manufacturer typically includes a main to printed circuit board (commonly referred to as the xe2x80x9cmotherboardxe2x80x9d) on which fixed system components are mounted. These fixed system components may include a microprocessor (as referred to as a processor), random access memory (RAM), read only memory (ROM), expansion slots, etc. Linking all of these fixed system components that are mounted onto the motherboard are a series of system buses. One particular system bus included on the motherboard is the local system bus. The local system bus is a bus used by the microprocessor. One advantage of the local system bus is that it may communicate with the microprocessor at the microprocessor""s speed, which typically is the fastest operating fixed system component.
Another type of system component located on the motherboard is an expansion component. Expansion components are used to provide additional functionality to the computer system. Thus, when the local system bus is connected between the microprocessor and another system component, such as the expansion slots with expansion components like video and drive controller cards attached thereto, the overall performance of the expansion component is greatly enhanced.
In order for the computer system to operate, a power supply is coupled to the motherboard to supply power. The power supply sends power to all of the other system components through its own bus. With an increasing popularity of mobile computers, as evidenced by a growth in a market for so-called xe2x80x9cnotebookxe2x80x9d or xe2x80x9claptopxe2x80x9d computers, power consumption has become an important consideration for computer designers. Power conservation efforts have been directed at virtually every aspect of such computers, including hardware, firmware and software. For example, most of today""s popular processors, such as Intel""s Pentium(copyright) family of processors, are capable of operating in a low-power mode. In addition, many computer systems now include power management functionality as part of an installed BIOS (Basic Input-Output System). Software developers are also becoming more power-conscious, writing xe2x80x9cgreenxe2x80x9d applications which are themselves power efficient while cooperating with the aforementioned hardware and firmware facilities.
One of the problems faced by computer designers, firmware developers and software developers with respect to power management is the use of expansion components that require power when the computer system is in a low power state. For example, expansion components may include monitoring circuitry used to monitor the temperature or the voltage of the computer system when the computer system is operating in a normal-power mode or in a low-power mode. This monitoring circuitry provides information to a remote location which can be part of a local area network (LAN).
When the computer system operates in a low-power mode, most fixed system components are switched off and the microprocessor is either switched off or operates at reduced power. However, expansion components connected to same local system bus as the switched off fixed system components, are negatively affected by these components because the switched off component may drain power from the local system bus.
There is presently no satisfactory solution to the problem of an expansion component properly operating when the computer system is in a low-power mode.
In accordance with an embodiment of the present invention, a computer system allows an expansion component of the computer system to operate even when the computer system is in a low-power mode. According to an embodiment of the present invention, a local system bus includes a first section and a second section. An isolation circuit is included which selectively establishes a connection between the first section of the local system bus and the second section of the local system bus during a normal-power mode of the computer system and removes the connection between the first section of the local system bus and the second section of the local system bus during a low-power mode.